The present invention generally relates to mobile communication systems and methods for signaling in mobile communication systems and, more particularly, to systems and methods for communicating voice message notifications between mobile communication systems which operate according to different, incompatible, protocols.
Voice mail systems (VMS) enable a subscriber to receive messages when the subscriber is unable to take a telephone call. VMS's are very popular among cellular telephone users because they allow people to leave messages for the cellular telephone user, when the user is unavailable, e.g., the cellular telephone has been turned off. As cellular technology has advanced, various methods have been devised for alerting a cellular telephone subscriber that a voice mail message has been received.
One type of cellular communication system is known as the Global System for Mobile Communications (GSM). The GSM describes what was originally a European standard (and now is being used in many areas of the world) for mobile communication which is intended to provide uniformity so that users can access different mobile communication systems with minimal equipment compatibility problems. The GSM network normally uses the Short Message Service (SMS) to notify a mobile station that a voice mail message has been received by the VMS. SMS is a message function service which provides for the transmission of short text messages having up to, for example, 160 alphanumeric characters to be sent to a subscriber at his or her mobile unit. For a more complete discussion of SMS in GSM systems the interested reader is referred to U.S. patent application Ser. No. 08/779,642, Astrom et al., which is herein incorporated by reference and to GSM T.S. 03.40.
FIG. 1 is a node diagram illustrating the signaling between nodes in a GSM system when a service center (SC) receives a voice mail message for a subscriber. When the SC receives a voice mail message for a subscriber, the SC sends an SMS message containing a voice message notification to the service center/gateway mobile switching center (SC/GMSC). Upon receipt of the SMS message with a voice message notification, the SC/GMSC sends a send routing information (SRI) for the short message (SM) to the GSM home location register (HLR). The HLR sends the routing information back to the SC/GMSC in an SRI for SM acknowledgment (ACK). Using the routing information received from the HLR, the SC/GMSC forwards the voice message notification to the mobile switching center/visited location register (MSC/VLR) where the subscriber is currently located, in a mobile terminated (MT) Forward SM message. Upon receipt of the MT Forward SM message, the MSC/VLR attempts to contact the mobile station, (not shown), in order to notify the mobile station that the subscriber has received a voice message. After attempting to notify the mobile, a MT Forward SM ACK message is sent to the SC/GMSC containing an indication of whether the VLR/MSC has successfully communicated the voice message notification to the mobile station. The SC/GMSC then sends a SMS ACK message to the SC indicating whether or not the voice message notification has been received by the mobile station.
Many cellular telephone networks in the United States use the IS-41 standard for signaling. The IS-41 standard defines, among other things, the use of a qualification directive message as a voice message notification to indicate to a mobile subscriber that the VMS has received a voice mail message for the mobile subscriber. FIG. 2 illustrates the signaling between nodes when an SC, located in a network which uses a signaling protocol in accordance with the IS-41 standard, receives a voice mail message for a subscriber. When the SC receives a voice mail message for a subscriber, the SC sends a VMS indication to an IS-41 HLR. The IS-41 HLR determines where the subscriber is currently located and sends a qualification directive to the visited mobile switching center (VMSC) where the subscriber is located. The VMSC then attempts to notify the mobile station (not shown) that a voice message has been received for the subscriber. The VMSC sends a qualification directive ACK to the IS-41 HLR indicating whether or not the mobile station has received the voice message notification. The IS-41 HLR sends a VMS indication ACK to the SC indicating whether or not the mobile station has received the voice message notification.
Dual mode cellular telephones have been developed to allow people who travel between different cellular systems to use a single cellular telephone in both systems. Accordingly, if a European businessperson travels between Europe and the United States often, then the businessperson would purchase a dual mode cellular telephone which can operate according to air interface standards of both systems. In order to allow roaming between different systems, network providers have set up roaming agreements such that the European businessperson can make telephone calls while roaming in the United States and the telephone calls will be billed to the businessperson's account with the European cellular provider.
In order to perform protocol adaptation for signaling between different cellular communication networks and to provide various other functions for intersystem roaming an interworking function (IWF) is used. For instance, in the aforementioned example the IWF allows the businessperson's account to be billed for the out of system telephone calls, e.g., the calls made in a network which operates according to the IS-41 protocol. For example, U.S. Pat. No. 5,610,974 issued to Lantto, which is herein incorporated by reference, teaches an IWF wherein a user of a first mobile network which operates according to a first protocol can receive calls while the user is located in an area served by a second mobile network which operates according to a second protocol using the same telephone number which is used to reach the user in the first network.
However, roaming agreements and dual mode cellular telephones still fail to provide the European businessperson with the ability to be notified of the receipt of voice mail messages by the VMS while roaming in a network which uses an IS-41 protocol. Accordingly, the businessperson must continually call the VMS, in his home network, to determine whether any new voice mail messages have been received. This can be very time consuming and expensive.
From the foregoing, it is apparent that conventional techniques for roaming between two mobile networks which operate according to different signaling protocol standards fail to provide voice message notifications to roaming subscribers. Accordingly, it would be desirable to provide a method and system which allow voice message notifications to be received while a mobile subscriber to a first network which operates according to a first protocol is roaming in a second network which operates according to a second protocol.